Tape cartridges configured to meet certain minimum physical requirements are said to have a particular "form factor." In the tape cartridge arts, form factor generally defines the peripheral dimensions of the cartridge and the interface characteristics with the tape drive. For a variety of economic and manufacturing reasons, it may be desirable to provide a tape cartridge for a different type of tape drive that has the same form factor as existing tape cartridges. If there are different recording and dimensional characteristics of the magnetic tape for the different tape drive, however, such a tape cartridge must be distinguishable from existing tape cartridges of the same form factor.
Current techniques for distinguishing between different tape cartridges having the same form factor typically rely either on the read/write head assembly to magnetically detect a non-conforming tape format, or on some type of interaction between a physical feature of the tape cartridge and a sensing circuit in the tape drive. European Patent Application 0 389 121, for example, describes a data protection feature for a tape cartridge that enables sensing circuitry within the tape drive to distinguish between two different types of tape cartridges in otherwise identical form factors.
U.S. Pat. No. 5,480,103 (Gerfast et al.) discloses mutually incompatible mechanical cartridge lockout mechanisms incorporated into tape cartridges of the same form factor to mechanically distinguish between tape cartridges containing magnetic tape with different recording characteristics. In operation, the first tape cartridge can not be inserted into the tape drive for reading the second tape cartridge. Conversely, the second tape cartridge can not be inserted into a tape drive for reading the first tape cartridge.
Digital linear tape drives of the type sold under the "DLTtape" trademark are the most popular backup drives on the market today. As the drive and cartridge technology evolves to incorporate magnetic tapes with different recording characteristics, it is desirable for the new drives to be backwardly compatible with the enormous number of existing digital linear tape cartridges in use. In some circumstances, however, a fail-safe mechanical incompatibility is necessary to prevent new tape cartridges with magnetic tape having different recording characteristics for the new tape drive from being inadvertently used in an older style tape drive that might destroy data written on the tape by a newer drive.